Gas or vapor discharge device



Oct. 31, 1939. w ELENBAAS 2,177,694

GAS on VAPOR DISCHARGE DEVICE Filed D86. 29, 1936 Fig.1.

Inventor: Willem Elenbaas,

' Attorney Patented Oct. 31, 1939 PATENT OFFICE GAS OR VAPOR DISCHARGEDEVICE Willem Elenbaas, Eindhoven, Netherlands, as-

signor to General Electric Company, a corporation of New YorkApplication December 29, 1936, Serial No. 118,129 In the NetherlandsJanuary 24, 1936 1 Claim.

This invention relates to gas or vapor discharge devices, and moreparticularly to such devices as are adapted to operate with anelectrically constricted arc discharge. vention to reduce the startingpotential of such a discharge device by the addition of a startingmedium which does not seriously increase the loss of heat irom thedischarge are to the enclosing envelope.

It is known to improve the starting of a vapor lamp, such as a mercurylamp, by the addition of a gas, for example, argon, to the mercuryvapor. If one substance of such a mixture has a first excitation orresonance potential above the ionizing potential "of the othersubstance, starting may occur at a lower voltage than would be possiblewith either substance ernployed alone. (It may be noted that theresonance potential of a medium is a measure of the electron energyrequired to raise atoms of the medium to a socalled excited conditionfrom which they may return to the normal state with an accompanyingrelease of energy.) The phenomenon of low voltage starting, which isdescribed by F. M. Penning in Zeitschrift fur Physik, vol. 46,.pages 335et seq., is believed to be attributable to the ionization of thesubstance of lower ionizing potential by energy derived from excitedatoms of the other substance.

It has been observed in connection with mer-w oury vapor lamps using asingle starting gas that invention to use with the mercury a mixture oftwo fixed gases whose excitation and ionization potentials are in thedesired relation to one another.

In using a starting gas with vapor lamps adapted to operate with aninternal pressure above atmospheric and, particularly, in the rangebetween one and about ten atmospheres an unexpected difficulty isencountered in that the addition of such a gas tends to decrease theemciency of the discharge.- This is explainable by the fact that at thepressures specified the normal dis charge occurs as an intense arcconstricted in cross-section by the prevailing electrical conditions.The luminosity of such an arc depends largely upon its temperature,which in turn is governed by the rate of heat transfer to the walls ofthe enclosing envelope. It is this latter factor which is adverselyaffected by the addition of other gaseous media to the discharge space.

It is an object of the in- In accordance with the present inventioneffective reduction in starting potential is accomplished withoutseriously increasing the heat loss by employing particular gases underoptimum pressure conditions. In particular a preferred 5 combination foruse with mercury comprises a mixture of neon with a small quantity, say0.2 per cent of argon. The total quantity of the fixed gases should beless than 6 and, preferably, less than 4 atom per cent of the quantityof mercury 10 vapor present in the device during operation, and thefixed gas pressure at room temperature should be less than 18millimeters and, preferably, less than 10 millimeters. The quantity atomper cent may be defined as 1 IOOX' T in which N1 is the number ofmercury vapor atoms present during the operation of the device and 20 N2is the number of fixed or starting gas atoms.

Some of the advantages realized by the use of this preferred mixture areindicated in Fig. 1 of the drawing, which shows the heat conduction fromthe arc discharge to the wall of the enclosing envelope as a function ofthe atom per cent of various starting gases. The thermal conduction inthe absence of a starting gas is assumed to be equal to 1. From theordinates it can be determined in a simple manner to what extent thedifierent gases increase the heat conduction to the boundary of thedischarge space. For instance, a helium filling of 10 atom per centcauses an extra heat loss of approximately 6''! per cent while an argonfilling of 10 atom per cent causes an extra heat loss of onlyapproximately 18, per cent.

It is apparent from Fig. 1 that the heat loss may be maintained belowabout 15 per cent, a permissible value, by using up to about 6 atom percent of neon. I have further determined that in so-called high pressuremercury discharge devices the addition of somewhat less than this amountof neon together with a fraction of a per cent of argon materiallydecreases the ignition or starting voltage of the discharge device. Thepermissible atom per cent'is somewhat variable with the operatingpressure of the mercury, but the gas pressure at room temperature shouldbe chosen below 18 millimeters and preferably below 10 millimeters inorder to maintain the heat loss within proper limits.

A particular application of the invention is shown in Fig. 2 whichillustrates schematically a discharge 'device primarily intended asalight 58 source. This device consists of an envelope I in which thedischarge takes place, cooperating electrodes 2 and 3 adapted to receivethe discharge and an auxiliary electrode 4 useful in initially startingthe device. It will be noted that the auxiliary electrode 4 is connectedto the current supply wire of the electrode 3 through a resistance 5.The envelope l is placed in an evacuated enclosure 6 which is providedwith a base 1 having contacts to which the two discharge electrodes areconnected. During operation these base contacts are connected to acurrent source 9 through a series impedance 8;

The envelope I preferably contains about 7 milligrams of mercury percentimeter of envelope length. During operation all of the mercury isevaporated so that unsaturated mercury vapor at a pressure of about 1atmosphere is present in the envelope. In addition, the envelopecontains a quantity of neon to which about 0.2 per cent of argon hasbeen added, the pressure of these combined gases at room temperaturebeing about 3 millimeters. The spacing between the electrodes 2 and 3 is150 millimeters while the inside diameter of the envelope I is 28millimeters. The current, which can be regulated by means of the voltageof the current source 9 and impedance 8,

is 3.5 amperes while the voltage between the electrodes is 130 volts.From these data it can be shown that the quantity of starting gas isabout 3 atoms present of the quantity of mercury vapor per cent in theenvelope during operation.

While I have described the invention in connection with a particulardischarge device, it is also applicable to devices in which an excess ofmercury is present and can be applied in connection with devicesinvolving very high mercury pressures, for example, pressures higherthan 10 atmospheres. I therefore aim in the appended claims to cover allsuch modifications as fall within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

An electric gaseous discharge device comprising a sealed tubularenvelope having a pair of main operating electrodes sealed into oppositeends thereof, an auxiliary electrode sealed into said envelope adjacentone of said main electrodes, said auxiliary electrode being connectedthrough a resistance to the other of said main electrodes, mercurywithin said envelope in an amount suiiicient to produce a pressure ofsubstantially one atmosphere when wholly vaporized; and a gaseousfilling within said envelope of neon intermixed with 0.2% of argon at apressure of the order or 3 mm., in combination with means to supplysufflcient electrical energy to said device to wholly vaporize saidmercury.

WILLEM ELENBAAS.

